1. Field of the Invention
This disclosure relates to a light emitting device control circuit device and a method to control the control circuit device which drives light emitting devices in a time-shifted manner with respect to one another (i.e., a ON-OFF timing of the light emitting devices is shifted with respect to one another) to avoid concentration of current consumption at predetermined timing, and to prevent noise caused by an increase of current consumption.
2. Description of Related Art
As for a semiconductor device well known as a light emitting device or a display device, a light emitting diode (LED) or an organic light emitting diode (OLED), and a laser diode (LD) are known. For example, the light emitting device can be used for a cell phone, a watch, a character display, an ornament, and so on.
FIG. 5 illustrates an image creating device described in FIG. 1 of the first related art (Japanese publication number 2001-343936). As a display device of the image creating device, a dynamic LED driver constructed with a 4-by-3 LED matrix included in a manipulation panel, is illustrated. The dynamic LED driver illustrated in the first related art is a technique to reduce energy consumption of the manipulation panel using LEDs provided as a matrix.
In FIG. 5, the dynamic LED driver includes a common driver 1 consisting of four PNP transistors TR0 to TR3, LEDs 2 provided as a 4-by-3 matrix, current restriction resistors 3 to control a current flowing to LEDs for respective light emitting colors (i.e., green[G0, G1, G2, G3], red[R1, R1, R2, R3], and yellow[Y0, Y1, Y2, Y3]) and a data driver 4 consisting of three NPN transistors (TRG, TRR, TRY). The LEDs 2 are driven by a common driver 1 and a data driver 4.
The CPU 5 controls the image creating device. To drive the driving transistors designated by the two drivers (i.e., the common driver 1 and the data driver 4) sequentially on a time division basis, the CPU 5 provides driving signals to output ports COM0 to COM3 and output ports DATA0 to DATA2 in response to a predetermined condition. The CPU 5 is a central processing unit to control the entire image creating device including the LED dynamic driver, in response to a program stored in ROM (Read Only Memory) 7 and RAM (Random Access Memory) 8.
The emitter of each of the PNP transistors TR0 to TR3 of the common driver 1 is connected to a 5 voltage power source, and the collector of each of the PNP transistors TR0 to TR3 is provided to a corresponding position of the LEDs 2.
Bases of the PNP transistors TR0 to TR3 are connected to respective corresponding output ports COM0 to COM3 of the CPU 5. Time division driving signals are provided from the output ports COM0 to COM3. If the time division driving signals are at a high level, the PNP transistors TR0 to TR3 turns to OFF state. If the time division driving signals are at a low level, the PNP transistors turn to ON state.
The PNP transistors TRG, TRR, and TRY of the data driver 4 are provided correspond to respective light emitting colors. Emitter of each of the transistors is connected to a ground, and each collector of the transistors is connected to cathode of the corresponding color LEDs via current restriction resistors RG, RR, and RY. Bases of the transistors TRG, TRR, and TRY are connected to output ports DATA0 to DATA2 of CPU5. If the time division driving signals provided from the output ports DATA0 to DATA2 are at a low level, the transistors TRG, TRR, and TRY change to OFF state. If the time division driving signals provided from the output ports DATA0 to DATA2 are at a high level, the transistors TRG, TRR, and TRY change to ON state.
Therefore, if a base voltage of any one of the PNP transistors TRi (i=0 to 3) of the common driver 1 is at a low voltage, and if a base voltage of any one of the NPN transistors TRj (j=G,R,Y) of the data driver 4 is at a high voltage, then a current flows to the selected LED (a LED located at [i,j]) and the selected LED is driven (i.e., illuminate).
In the first related art, first and second driving means to drive the light emitting diodes provided as a matrix sequentially (i.e., time division drive) are disclosed. In other words, the first related art discloses the composition that has a LED matrix 2 is connected in series between the common driver 1 and the data driver 4.
FIG. 6 illustrates a light emitting control circuit referred to in FIG. 1 of the second related art (i.e., International publication number WO2006-137273 applied for by an applicant of this application). Symbols indicating components of the figure are modified for the present application. The light emitting control circuit 600 includes a PWM control circuit 61, a step-up circuit 62, switches SW1 to SW3, and the constant current drivers K1 to K3.
A characteristic of the light emitting control circuit 600 illustrated in FIG. 6 is summarized below. The light emitting control circuit 600 to drive multiple light emitting devices D1 to D3 includes current source circuits K1 to K3 which supply currents Io1 to Io3 to the light emitting devices D1 to D3. The light emitting control circuit 600 is provided correspond to the light emitting devices, and includes switches SW1 to SW3 corresponding to the light emitting devices. The switches SW1 to SW3 operate to connect or disconnect the current source circuits K1 to K3 to the respective light emitting devices D1 to D3. The light emitting control circuit 600 also includes a PWM control circuit 61. The PWM control circuit 61 supplies currents to the light emitting devices from the current source circuits intermittently by controlling the switches SW1 to SW3, and drives (i.e., switches a state from inactive to active) the light emitting devices in a time-shifted manner.
In the second related art (WO2006-137273), to supply a current to the light emitting devices D1 to D3, the switching from inactive state (the stop condition of the current supply) to active state (the start condition of the current supply) is performed in a time-shifted manner. Thus, same as the first related art, the second related art discloses a controller to drive the light emitting devices sequentially (i.e., time division drive).
FIG. 7 illustrates a LED driving device shown in FIG. 1(a) of the third related art (Japanese publication number 2008-91311), symbols indicating components of the figure are modified and added, and a part of FIG. 1(b) of the third related art is added for the present application.
In the third related art (Japanese publication number 2008-91311), LEDs are used as a backlight of a LCD (Liquid Crystal Display) and illuminations, when driving the LEDs by pulse width signals to control a brightness, prevent noise caused by simultaneous drive of the LEDs connected in parallel with each other. The third related art also discloses a stable operation even when a sudden increasing of an illumination output is occurred.
In FIG. 7, the LED driving device 700 includes a LED illumination part 71, and a LED driving controller 72 to drive the LED illumination part 71. The LED illumination part 71 includes LED groups LEDG1 to LEDG5 connected in parallel with each other. Each of the LED groups consists of LEDs connected in series. A current is supplied from a power source 73 to the LED illumination part 71, and transistors Tr.1 to Tr.5 (as switching elements) are connected to respective ground terminals of the LED groups LEDG1 to LEDG5. These transistors Tr.1 to Tr.5 are driven by the driving signals DRV1 to DRV5 provided from the PWM (Pulse Width Modulate) controller 74 which provides driving pulses in response to a control direction signal S.
With respect to the PWM controller 74, if a control direction signal S to indicate an illumination brightness of the LEDs is provided to the PWM controller 74, the PWM controller 74 provides PWM driving signals DRV1 to DRV5 in response to the control direction signal S. The PWM controller 74 divides one cycle of a driving signal by the number of the LED groups, and outputs driving signals DRV1 to DRV5, respectively, in accordance with division. In FIG. 7, the number of the LED groups is five, so one cycle (T) of a driving signal is divided by five. The driving signal DRV1 to drive the transistor Tr.1 (i.e., the first transistor Tr.1 drives the LED group LEDG1) is raised at rise time t1. The driving signal DRV2 to drive the transistor Tr.2 (i.e., the second transistor Tr.2 drives the LED group LEDG2) is raised at a timing which is delayed T/5 compared to the rise time t1. The driving signal DRV3 to drive the transistor Tr.3 (i.e., the third transistor Tr.3 drives the LED group LEDG3) is raised at a timing which is delayed T/5 compared to the timing of the rising of the driving signal DRV2. The driving signal DRV4 to drive the transistor Tr.4 (i.e., the fourth transistor Tr.4 drives the LED group LEDG4) is raised at a timing which is delayed T/5 compared to the timing of the rising of the driving signal DRV3. The driving signal DRV5 to drive the transistor Tr.5 (i.e., the fifth transistor Tr.5 drives the LED group LEDG5) is raised at a timing which is delayed T/5 compared to the timing of the rising of the driving signal DRV4. Thus LEDs are driven sequentially (i.e., time division drive) in response to the number of the LED groups.
In the first related art (Japanese publication number 2001-343936), both the supplied voltage and current to the light emitting diode are driven sequentially (i.e., time division drive). However, driving the multiple light emitting diodes with a delay (i.e., a period of the delay equals a part of one cycle of the pulse current drive) with respect to each other is not described.
In the second related art (WO2006-137273), supplying a current to the light emitting device sequentially (i.e., time division drive) is disclosed. However, supplying both a current and a voltage to the light emitting device sequentially is not disclosed. Also a technique to control each of the light emitting devices provided as a matrix pattern is not disclosed.
In the third related art (Japanese publication number 2008-91311), a technique to supply a current to the light emitting device sequentially (i.e., time division drive) is disclosed. However, supplying both a current and a voltage sequentially to the light emitting device (i.e., time division drive) is not disclosed. Also a technique to control each of the light emitting devices provided as a matrix pattern is not disclosed.
The light emitting device control circuit device of the present disclosure makes it possible to reduce energy consumption, and to prevent noise caused by the on/off switching of the light emitting devices in specific timing. The light emitting device control circuit device shifts ON-OFF timings of the light emitting devices provided as a m by n matrix pattern, and avoids overlapping the ON-OFF timings with respect to each other. Thus, a light emitting device control circuit device and a method to control the device are provided to avoid concentration of a current in a same timing.